1. Field of the Invention
The present invention relates to viscous fluid fan clutches such as clutches used in the automotive industry for controlling the amount of torque transmitted to a radiator cooling fan as a function of the temperature of a coolant fluid and, in particular, an anti-flowback check valve for the viscous fluid clutch which minimizes flowback of the viscous fluid from a reservoir to the working chamber of the fan clutch when the automobile is not being used and avoids excessive fan noise, wasted power and fuel inefficiency when a cold automobile engine is started.
2. Description of Related Art
Automobile fan clutches typically are “on-off” and “modulating” type devices and couple the cooling fan to the water pump. A fan clutch is activated by moving a viscous fluid in the clutch, typically, dimethyl-silicone from a storage chamber (reservoir) to a working chamber which couples a driving member to a driven member. The movement of fluid is controlled by mechanically opening or closing one or more ports in a plate that separates the storage chamber from the working chamber using typically a temperature sensing element or electromechanical means which moves a gate to open or close the ports. After performing its work during the circulation cycle, the ports are closed and the viscous fluid is returned to the storage chamber from the working chamber by pressure generated from shearing of the viscous fluid and centrifugal force. A passageway is provided to transport the fluid as the end of its useful stage in the working chamber to the reservoir.
The return passageway has an inherent problem when the automobile is stationary for a long period of time (for example, over night parking or storage) in that the passageway may be facing an orientation below the horizontal point. The fluid from the reservoir then has the ability to drain back from the reservoir to the working chamber. The probability for such orientation is as high as 50% and when the vehicle is then started any drained fluid in the working chamber will cause the fan clutch to engage resulting in excessive fan noise, wasted power and fuel inefficiency. With the fluid being at prevailing ambient conditions, the fluid has a relatively higher viscosity than compared to normal operations and the higher viscosity fluid thereby requires considerable time before it can work its way back from the working chamber to the storage chamber. This phenomenon is even more pronounced in cold weather conditions and is referred to as “morning thickness”.
To overcome this nuisance problem, manufacturers have included designs to minimize the amount of fluid drain back by orienting the return passageway at oblique angles. Other designs incorporate channels which are concentric to the storage chamber resulting in further reducing the amount of fluid to drain back. This design, though effective towards eliminating morning thickness, complicates the design by having to overcome the added resistance from the length of the channels. The channel has to be rotation specific or otherwise adds undue weight to the proper balance of the assembly.
In U.S. Pat. No. 5,022,507 issued to Kennedy et al. and assigned to General Motors Corporation, a viscous fluid fan clutch assembly is shown containing check valves in discharge channels to prevent the flowback of fluid from the reservoir to the discharge channels and into the working chamber, particularly when the clutch assembly is not in operation. This patent is hereby incorporated by reference.
U.S. Pat. No. 4,544,053 shows a temperature-responsive fluid coupling device for driving a cooling fan of an internal combustion engine and includes a ball check valve mechanism positioned in both the fluid return passage and a pumping passage. Springs are used to maintain the check valve in a closed position. U.S. Pat. No. 4,924,987 shows a fan clutch assembly wherein a check valve is provided in an orifice to control the flow of fluid that permits only one-way flow from the receiving chamber or working chamber into the reservoir. The check valve eliminates the migration of fluid through the orifice from the reservoir into the receiving or working chamber. The disclosures of both these patents are hereby incorporated by reference.
While the prior art has shown viscous fan clutches containing check valves and other mechanisms to prevent flowback of the fluid from the reservoir to the working chamber when the vehicle is not in operation, there is still a need for an enhanced fan clutch which will operate in a more efficient manner.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a viscous fan clutch which utilizes a check valve to minimize the flowback of fluid in the clutch from the reservoir to the working chamber.
It is another object of the present invention to provide a viscous fan clutch for an automobile which utilizes a check valve in the fan clutch to minimize flowback of fluid in the clutch from the reservoir to the working chamber when the automobile is at rest.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.